Polymers capsule manufacture

Gelatin capsules are manufactured by a dipping pro-cess. The process starts by the preparation of a concentrated solution of gelatin or other suitable polymer in hot demineralized water. This solution is subjected to a low pressure to remove entrapped air bubbles. Small aliquots of this solution are (20-30 L) are taken. To this are added colorants, either solutions of soluble dyes or suspensions of pigments, preservatives, process aids, such as disodium lauryl sulfate solution, and water to adjust the viscosity. The final solution has a concentration of 25-30 wt%o of gelatin. This solution is then delivered to the capsule-manufacturing machine. 

More recently, the attention has moved to synthetic polymers with the aim being to produce capsules that will overcome the shortcomings of gelatin, particularly its moisture content. Two alternative materials have been offered by capsule manufacturers, starch and hydroxypropyl methylcellulose (HPMC). 

S-G photo-biodegradable polyethylene is now being used in a different way to reduce the pollution of water courses by fertilisers. By encapsulating the fertiliser in porous photo-biodegradable capsules fertiliser release times can be achieved from 40 days to one year. Nitrogenous fertiliser based on this principle are manufactured by Chisso-Asahi Fertilizer Company of Japan and scientific studies by Kawai of Okayama University have shown (personal communication) that the empty polymer capsules biodegrade rapidly in soil. 

The development of HPMC capsules is achieved by three specialized companies. The first is Shin-Etsu Chemical Co., Ltd. which specialized in a field of polymer science. The second is Shionogi Co., Ltd., an innovative pharmaceutical company and the last is Shionogi Qualicaps Co., Ltd., ahard capsule manufacturer. In particular, I very much appreciate of Dr. N. Muranushi s (Shionogi Co., Ltd.) kindly supports. 

In addition to graft copolymer attached to the mbber particle surface, the formation of styrene—acrylonitrile copolymer occluded within the mbber particle may occur. The mechanism and extent of occluded polymer formation depends on the manufacturing process. The factors affecting occlusion formation in bulk (77) and emulsion processes (78) have been described. The use of block copolymers of styrene and butadiene in bulk systems can control particle size and give rise to unusual particle morphologies (eg, coil, rod, capsule, cellular) (77). 

The solvents used to dissolve the polymeric materials are chosen according to the polymer and drug solubilities and stabilities, process safety, and economic considerations. Substances can be incorporated within microspheres in the liquid or solid state during manufacture or subsequently by absorption. Fig. 1 shows two types of microspheres Microcapsules, where the entrapped substance is completely surrounded by a distinct capsule wall, and micromatrices, where the entrapped substance is dispersed throughout the microsphere matrix. 

It is now straightforward (see also Part V, Chapter 6) to fill the capsule not only with air, but a dmg substance too, and to use an ultrasound pulse to trigger the release from outside the body at a defined place and time by bursting the bubble. Utilizing nanotechnological concepts of polymer, colloid and interface science we have established a novel process to manufacture gas-filled microcapsules. On demand, gas filling, elasticity, shell thickness and overall size can be tailored independently. 

HPMC capsules are commonly made using low-viscosity grades of HPMC 2910 or 2906. HPMC and other materials are suspended in hot water, and subsequent decrease in water tanperature then allows the polymer to dissolve. Heated metal pins are then submerged into the concentrated solution. The heated pins cause local gelling of the polymer solution, leaving them coated with a thick film upon removal. Film coalescence occurs upon evaporation of water, and the resulting capsule half-shells are removed from the pins. Refer the book by Podczeck and Jones for more details on manufacturing of capsules. ... 

Despite the well known advantages of controlled release dosage forms, conventional dosage forms are still most widely used probably because they cost less to manufacture. More than three quarters of all drug formulations are made for oral administration. Oral dosage forms such as tablets, capsules, and liquids are still most popular. Since tablet is one of the most widely used dosage forms and its preparation requires incorporation of polymers, we will focus on polymers used in tableting process. 

A trend of recent years has been to supply additives processed into safe forms, in pellets, capsules, liquids and masterbatch concentrates and so, for the compounder and processor, the hazards have largely been taken out, but it is still important that they should be aware of them. For most compounders and processors of thermoplastics, the hazard from additives can now be safely contained upstream, during manufacture of the additives. In moulding and fabricating wet polymer systems, such as polyesters and polyurethanes, however, it is essential to take precautions. 

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